G. COTT, D. REIDY, D. CHAPMAN, M. JANSEN
Saltmarshes on peat substrate on the
southwest coast of Ireland: edaphic
parameters and plant species distribution
Grace M. COTT, Darren T. REIDY, Deborah V. CHAPMAN, Marcel A. K. JANSEN
School of Biological, Earth and Environmental Sciences, University College Cork, Cork, Ireland,
[email protected], [email protected], [email protected]
Abstract. Saltmarshes on peat substrate are common along the western Atlantic coast of Ireland. The peat which underlies these marshes was formed under freshwater conditions in post glacial times, after which these systems were subjected to a marine transgression. The aim of this study was to determine
the relationship between edaphic factors, substrate type and saltmarsh vegetation, specifically investigating the role of edaphic factors in determining
the distribution of saltmarsh species Atriplex portulacoides in Ireland. Edaphic parameters measured for each substrate included pH, moisture content,
ammonium and nitrate. The peat was found to differ markedly from other substrates. Using canonical correspondence analysis it was found that pH and
ammonium were the major drivers in influencing saltmarsh vegetation on peat substrate. Under both in situ and ex situ conditions Atriplex portulacoides
showed an affinity for drier substrate and its absence from fringe marshes in Ireland is likely due to a combination of both biotic and abiotic factors, including intolerance to high soil moisture levels.
Key words: saltmarsh vegetation, peat, edaphic properties, Atriplex portulacoides
1. Introduction
Saltmarshes develop on low energy coasts and have
been defined as areas arising from the accretion of sediments
or the accumulation of organic matter in situ under the influence of the tide (Chapman, 1960; Beeftink, 1977). This definition, however, does not account for all types of saltmarsh. In
particular, this definition is not suitable to define those saltmarshes that have formed on non-marine substrates such as
peat. Such saltmarshes are common along the Irish western
seaboard. A complete inventory of all saltmarshes in Ireland
was carried out, which classified them according to their
morphology and nature of the substrate (Curtis and Sheehy
Skeffington, 1998). Out of the 250 saltmarshes surveyed, 57
were found to have an underlying peat substrate. The term
‘fringe saltmarshes’ was proposed to describe saltmarshes on
peat substrate.
Fringe saltmarshes occur in sheltered rocky bays or in
narrow bands between the sea and heath dominated hinterland. The peat which underlies these marshes was formed
under freshwater conditions in post glacial times (10,000 B.P.)
when climatic conditions resulted in the formation of ombrogenic blanket bogs and the accumulation of thick layers
of peat (Sheehy Skeffington and Curtis, 2000). These blanket bogs developed to the greatest extent in regions with a
pronounced oceanic climate, giving rise to a high density of
these marshes along the western Atlantic seaboard (Mitchell, 1986). The blanket bogs are predominantly made up of
Sphagnum-Molinia type peat in the upper horizons and some
contain wood peat, incorporating birch and alder remains,
in the lower horizons (Jessen, 1948). A subsequent marine
transgression resulted in a shift from freshwater conditions
to saline conditions for some of the blanket bogs. This transgression is estimated to have occurred between 4000 and
2000 B.P. (O’Connell, 1988).
Marshes on peat substrate can also be found in Scotland
and other parts of North Atlantic Europe (Adam, 1990). However, in these marshes, peat was formed under the influence
of the sea (Sheenan, 1995; Allen, 2000). Thus, the ontogeny of
Irish peat (fringe) marshes is essentially different, consisting
of a clearly distinct freshwater phase of peat formation, followed by a marine dominated period.
Geo-Eco-Marina 17/2011
41
G. Cott, D. Reidy, D. Chapman, M. Jansen – Saltmarshes on peat substrate on the southwest coast of Ireland: edaphic parameters and plant species distribution
The peat saltmarshes of Ireland are unique in their ontogeny, as well as their vegetation. To date, these systems have
not been studied in any detail, nor have they been compared
with non-fringe systems. Three other types of substrate are
predominant in Irish saltmarshes. These are sand, associated
with sand flats and sand dunes systems; mud, associated with
estuarine saltmarshes; and a mixture of sand/mud, which can
be associated with bay, estuarine and dune systems (Curtis
and Sheehy Skeffington, 1998). Invariably these substrates
have different edaphic properties compared with peat,
but the degree to which they differ and the consequences
thereof, are unknown. It has long been recognised that the
vegetative community at a particular site is determined by
environmental controls, comprising both biotic and abiotic
influences, resulting in a community that is capable of stable
co-existence under such conditions. Abiotic factors that distinguish saltmarshes from many other terrestrial and aquatic
systems include waterlogging, acidity or alkalinity, salinity,
and the availability of nutrients.
It has been observed that the common saltmarsh shrub
Atriplex portulacoides (L.) Aellen (previously known as Halimione portulacoides) is largely absent from the fringe marshes on the west coast of Ireland, while being locally abundant
on the east coast (Sheehy Skeffington & Curtis, 2000) (Figure
1). It had been hypothesised by Sheehy Skeffington & Curtis
(2000) that relatively intensive grazing on the west compared
with the east coast was the limiting factor for the distribution
of A. portulacoides in Ireland. Grazing can seriously inhibit
growth and prevents A. portulacoides becoming dominant
(Dormann et al., 2000; Van Wijnen et al., 1999), but species are
rarely completely excluded as a result of grazing practices.
suggested that fringe marshes may be poorly drained and
water logged, as is the typical nature of reed swamps and
peat substrates (Montemayor et al., 2008). Consequently, it
can be hypothesized that the distribution of A. portulacoides
on salt marshes is limited by soil waterlogging, and that A.
portulacoides is excluded from the west coast of Ireland due
to the predominance of poorly drained fringe systems on
peat substrate.
The aim of this study was to determine relationships between edaphic factors, substrate type and saltmarsh vegetation in fringe marshes on the west coast of Ireland. Specifically the role of edaphic factors in determining the distribution
of the saltmarsh species A. portulacoides, under in situ and ex
situ conditions, was investigated.
2. Materials and Methods
2.1. Field sampling
Study sites were selected on the basis of their classification in Curtis and Sheehy Skeffington (1998). One saltmarsh
on each of four substrates: peat, sand, mud and sand/mud,
was chosen for this study. These sites were located at Ahakista (51º35’56”N, 09º36’6.2”W), Ballyheigue (52º21’31”N,
09º50’13”W), Timoleague (51º38’29”N, 08º45’37”W) and
Kilbrittain (Harbour View) (51º39’10”N, 08º40’23”W) respectively.
Fig. 2 Map of four selected saltmarsh sites on different substrates
in southwest Ireland: sand located at Ballyheigue, Co. Kerry, peat
(fringe marsh) at Ahakista Co. Cork, mud at Timoleague, Co. Cork
and sand/mud at Kilbrittain (Harbour View), Co. Cork.
Fig. 1 Map of Ireland showing the location of fringe saltmarshes
and Atriplex portulacoides. (Adapted from Sheehy Skeffington and
Curtis, 2000)
Evidence exists to support the theory that the distribution of A. portulacoides is limited by waterlogging, aeration
and tidal inundation. Based on their ontogeny, it has been
42
At each site nine quadrats were sampled: three in the upper, middle, and lower shores, during April and June 2009.
The size of the quadrat for vegetation analysis was 2 × 2m
based on the concept of minimal area study (Kent and Coker,
1992). Species were identified and percentage cover recorded for each quadrat. Soil cores were taken at each quadrat
using a 5cm diameter soil auger. The cores were taken to a
depth of 15cm. Soil samples for available nitrogen analysis
were homogenised and frozen as soon as possible as rec-
Geo-Eco-Marina 17/2011
G. Cott, D. Reidy, D. Chapman, M. Jansen – Saltmarshes on peat substrate on the southwest coast of Ireland: edaphic parameters and plant species distribution
ommended by ISO/TS 142560-1 (2003). Soils were extracted
with 1M KCl (ISO/TS 142560-1, 2003). Subsequent analyses of
nitrate and ammonium were carried using automated Flow
Injection Analysis (Lachat Quikchem IC+FIA 8000) by the
accredited Aquatic Services Unit laboratory at UCC. pH was
determined in aqueous suspension 1:2 soil:water ratio (Allen,
1989) using an Orion 3 soil pH meter (Thermo Electron Cooperation, Singapore). Moisture content was measured gravimetrically and the soil was oven dried at 40°C to a constant
weight (Allen, 1989). Both the soil sampling and vegetation
analyses were carried out at each site over consecutive days
in order to minimise the effect of environmental variables,
such as weather, and also to sample at similar times of the
tidal cycle. Sampling began at low tide each day so that results were comparable between sites.
2.2. Ex situ growth experiment
In order to examine the influence of substrate and/or
waterlogging on the growth of A. portulacoides an ex situ experiment was carried out. Cuttings of approximately 3 to 5cm
length were taken from Kilbrittain saltmarsh, Co. Cork. These
were planted in prepared seed trays containing a rooting medium of potting compost, washed sand, and perlite. Cuttings
were watered with freshwater to aid establishment. After five
weeks healthy root systems had developed sufficient to conduct the growth experiments. One week prior to the experiment seedlings were watered with varying concentrations of
seawater gradually increasing to 35ppt.
Peat substrate for the experiment was extracted from a
fringe marsh at Schull, Co. Cork (51º30’46”N, 09º35’7”W) and
sand substrate was also taken from Kilbrittain saltmarsh. The
peat and sand were then transferred to flower pots of 8cm
diameter. In each pot a single rooted cutting was planted and
all pots were kept in a glass house with a photo period of 16
hours light (18ºC) and 8 hours dark (10ºC). Four submergence
treatments using seawater were carried out on both peat
and sand substrate. These comprised constant submergence,
submergence for 24 hours twice a week, submergence for 1
hour twice a week and a control which was watered when
required. The experiment was conducted for 5 weeks before
plants were harvested, after which changes in root and shoot
length, biomass and leaf number were measured as growth
responses.
2.3. Statistical analysis
To improve homogeneity of variance, moisture data,
ammonium and nitrate data were transformed (arcsine and
natural log respectively) prior to analysis. A oneway ANOVA
was carried out using SPSS (PASW® Statistics 17) software. Differences in means (p<0.001) were assessed by Bonferonni ad
hoc comparisons.
To establish the relationships between plant species and
spatial–temporal changes in edaphic variables, canonical cor-
respondence analysis (CCA) (ter Braak, 1987) was performed
using the Multi-Variate Statistical Package (MVSP) program
Version 3.1 (Kovach Computing Services). Species data were
square root transformed prior to analysis.
For the growth experiment two Interaction ANOVAs were
conducted for each growth response for plants grown in
sand and peat substrates. Both were compared to identify the
influence substrate and submergence would have. A Tukey
test was used to identify where any significant relative difference in shoot length, root length, overall biomass or leaf
number lay. This allowed differences between treatments to
be identified, but also identified the significance of substrate
and submergence regime on these results.
3. Results
3.1. Edaphic parameters
Peat has the lowest pH of the four substrates that were
tested, averaging at 6.55. The highest pH value was obtained
for the sand substrate, averaging at 8.52 (Figure 3(a)). One
way ANOVA revealed that there were significant differences
in pH between the four substrates F(3,67)=112.28, p<0.001.
Bonferroni comparisons showed that the pH of peat was significantly lower (p<0.001) compared with that of sand, mud
and sand/mud. The pH of the mud substrate was also significantly lower compared with that of sand and sand/mud substrates. The pH of sand substrate was not significantly different to that of sand/mud.
The peat substrate was found to have the highest moisture content followed by mud, and then sand/mud. Sand
substrate had the lowest moisture content (Figure 3(b)). Oneway ANOVA showed that there were significant differences in
moisture content between the four substrates F(3,69)=148.68,
p<0.001. Bonferroni comparisons showed that peat substrate has a significantly higher moisture content than sand
or sand/mud. There was no significant difference in moisture
content between peat and mud substrate. Sand has a significantly lower moisture content than mud but not sand/mud
substrate.
Ammonium content also differed significantly between
the four substrates F(3,67)=46.46, p<0.001 (Figure 3(c)). Peat
substrate contains up to three times more NH4 than the other
substrates. Bonferroni comparisons revealed that NH4 content in peat is significantly higher (p<0.001) compared with
sand, mud and sand/mud substrates.
Significant differences in nitrate levels were also detected
between the four substrates F(3,57)=49.23, p<0.001. Nitrate
levels were found to be significantly higher in peat compared
with mud and sand/mud substrates (Figure 3(d)). Although
peat substrate contained substantially more nitrate than
sand substrate, this difference was not significant.
Geo-Eco-Marina 17/2011
43
G. Cott, D. Reidy, D. Chapman, M. Jansen – Saltmarshes on peat substrate on the southwest coast of Ireland: edaphic parameters and plant species distribution
Fig. 3 (a) pH, (b) moisture content, (c) ammonium (NH4) and (d) nitrate (NO3) content of saltmarsh substrates, peat, sand, mud and sand/mud.
Each value is mean ± SE (n=18). Bars with same letter are not significantly different by Bonferroni at 0.001 level.
3.2. Vegetation Analysis
Species abundance for each substrate is presented using
the Domin scale (Dahl and Hadăc, 1941) in Table 1. The relationship between the distribution of salt marsh vegetation
and edaphic variables was analysed using canonical corre-
spondence ordination. The most important variables which
explained variations in the vegetation data set were pH, ammonium and nitrate content (Figure 4). Both are strongly correlated with axis two. At the extreme end of the positive side
of axis 2, appear species which can tolerate high ammonium in
soils, Juncus maritimus, Juncus gerardii and Triglochin maritima.
Table 1. Plant species cover at each of the four saltmarsh sites in southwest Ireland (see Figure 2). Cover scale (Domin Scale) 1, <2% cover;
2, 2%cover; 3, 3% cover; 4, 4-10% cover; 5, 11-25% cover; 6, 26-33%; 7, 34-50% cover; 8, 51-75%; 9, 76-90%; 10, 91-100% cover.
Number
44
Species
Peat
Sand
Sand/Mud
Mud
1
Juncus maritimus
6
-
-
-
2
Puccinellia maritima
5
7
7
5
3
Juncus gerardii
5
-
-
3
4
Armeria maritima
4
-
4
-
5
Plantago maritima
7
3
4
5
6
Spergularia media
4
1
1
1
7
Glaux maritima
3
4
1
-
8
Triglochin maritima
4
-
-
1
9
Aster tripolium
4
5
4
5
10
Limonium humile
-
-
1
1
11
Cochlearia officinalis
3
5
1
5
12
Spartina sp.
-
4
4
5
13
Atriplex portulacoides
-
-
5
4
Geo-Eco-Marina 17/2011
G. Cott, D. Reidy, D. Chapman, M. Jansen – Saltmarshes on peat substrate on the southwest coast of Ireland: edaphic parameters and plant species distribution
Fig. 4 Canonical correspondence ordination of salt marsh vegetation in Southwest Ireland showing correlation between principal plant species
and edaphic variables. Species numbered according to Table 1. P, peat; s, sand; s/m, sand/mud; m, mud. Eigenvalues: axis 1, 0.301; axis 2, 0.123.
Species-environment correlation: axis 1, 1.00; axis 2, 1.00. Percentage cumulative variance of species–environment relation accounted for the
two first axes: 87.4%.
On the extreme of the negative side of axis 2, and correlating with increases in pH, appear Spartina sp. Near the origin
of the coordinates the most significant species are Plantago
maritima, Puccinellia maritima and Aster tripolium. Nitrate is
highly correlated with ammonium. Both A. portulacoides and
Limonium humile have the most negative scores. The peat
substrate is located on the positive axis, i.e. removed from
both A. portulacoides and Limonium humile.
plants was significantly greater than in plants on sand that
were constantly submerged (p<0.01), and substantially (but
not significantly) greater than observed in plants submerged
for 24hrs or 1hr twice weekly.
3.3. Growth experiment
To investigate further the negative relationships between
peat substrate, soil moisture content and A. portulacoides
distribution (Figure 4), the performance of A. portulacoides
plants under a range of inundation regimes were investigated. Plants grown in sandy or peat substrate and constantly
submerged in salt water were found to suffer a decrease in
root length, with an average loss of 13% and 22%, respectively. Root loss was not significantly different between the two
substrates (Figure 5(a)). The greatest percentage increase in
root length (121%) was found for plants grown in peat, submerged for 1 hour twice weekly, although this was not significantly greater than plants in peat watered only occasionally
(control). Nevertheless, the increase in root length when submerged for 1 hour twice weekly was significantly greater than
plants grown in peat that were submerged for 24hrs twice
weekly (p<0.05) or constantly submerged (p<0.001). When
plants were grown in sand substrate, those that were watered
occasionally exhibited the greatest increase in relative root
length. This increase in root length in occasionally watered
Fig. 5 Mean percentage change in (a) root length and (b) shoot
length of Atriplex portulacoides grown on sand and peat substrates for 5 weeks using seawater in treatments CS – Constant
submergence, 24hr- submergence for 24 hours twice weekly,
1hr- submergence for 1 hour twice weekly and Control - watered
occasionally. Each value is mean ± SE (n=10).
Geo-Eco-Marina 17/2011
45
G. Cott, D. Reidy, D. Chapman, M. Jansen – Saltmarshes on peat substrate on the southwest coast of Ireland: edaphic parameters and plant species distribution
On average, shoot length increased in all plants (Figure
5b). Interaction ANOVA found no significant influence of
substrate type on relative shoot growth. However, the interaction between substrate and submergence regime had a
significant influence on shoot length (p<0.05). Submergence
alone was also found to have a significant influence on relative shoot growth (p<0.001).
Plants grown in peat substrates, constantly submerged in
salt water exhibited the lowest percentage increase in shoot
length (23%). Percentage shoot growth increased as the time
spent submerged was reduced, such that plants on peat that
were occasionally watered with salt water exhibited the largest percentage increase in shoot length (95%). An interaction
ANOVA identified a significant difference (p<0.001) between
constantly submerged plants and the occasionally watered
controls. Plants that were submerged for only 24hrs or 1hr,
twice weekly, also displayed a significant increase (p<0.05)
in relative shoot length compared to those constantly submerged. Thus there was a strong tendency for relative shoot
growth to increase with a reduction in submergence. Plants
grown on sand submerged for 24hrs, twice weekly, displayed
a significant increase in shoot length (p<0.05) compared to
the other submergence regimes. Those submerged for 1hr,
twice weekly, or watered occasionally exhibited no significant difference in percentage growth to those constantly
submerged. The general trend was that shoot length for
plants on sand did increase, but not significantly, when submergence time was reduced.
submergence regimes and substrates. Interaction ANOVA
found that substrate had a highly significant influence on
relative change in biomass (p<0.01). Likewise submergence
was found to have a highly significant influence on relative
change in plant biomass (p<0.001). A significant interaction between substrate and submergence was also found
(p<0.05). A loss in plant biomass was observed in plants constantly submerged grown in both sand and peat. Plants that
were grown in sand and occasionally treated with salt water
displayed a significant increase in biomass (p<0.05) compared with those constantly submerged. Smaller increases
in biomass were observed in plants that were periodically
submerged. Overall, the general trend for plants raised on
sand substrate was for biomass to increase as submergence
was reduced. In contrast, when plants were raised on peat
substrate, the 24hr, 1hr and control treatments resulted in
a highly significant increase in biomass compared with the
constantly submerged sample (p<0.001). The trend was for
biomass to increase as submergence was reduced but no significant differences were found between 24hr or 1hr, twice
weekly, submergence or those watered occasionally.
Substrate type did not have an effect on the relative
change in leaf number of treated plants (interaction ANOVA).
Moreover, no significant interaction was found between substrate and submergence. In plants grown in sand and treated
with salt water an increase in leaf number was observed as
submergence was reduced. However, leaf numbers were not
statistically different across treatments.
4. Discussion
Substrate-linked edaphic factors were measured for four
types of saltmarsh substrate. Out of the four substrates studied it was clear that the peat substrate was the most distinct
with respect to edaphic factors. The edaphic properties which
distinguished the peat substrate from the other three substrates were low pH and high ammonium content. Typically,
the pH of terrestrial peat bogs is approximately 4.0 (Clymo et
al., 1984), whereas the pH of the peat substrate in the fringe
marsh was found to be 6.55. The pH difference may be due to
tidal inundation. Seawater can raise the pH of peat; bivalent
magnesium is the third most abundant ion in seawater, and
can be adsorbed by peat, resulting in a rise in pH (Sjörs and
Gunnarsson, 2002). Similarly, the higher pH of coastal blanket
bogs in Ireland compared with inland raised bogs has been
attributed to the effect of sea spray (Gorham, 1953; Sjörs and
Gunnarsson, 2002).
Fig 6 Mean percentage change in (a) biomass and (b) leaf number of Atriplex portulacoides grown on sand and peat substrates
for 5 weeks using seawater in treatments CS – Constant submergence, 24hr- submergence for 24 hours twice weekly, 1hr- submergence for 1 hour twice weekly and Control- watered occasionally. Each value is mean ± SE (n=10).
Total biomass was measured to quantify both above
and below ground productivity as a response to different
46
The biogeochemical cycling of nitrogen in wetland systems is complex. In anaerobic soils, ammonium-nitrogen is
the dominant form of available nitrogen (Huang and Pant,
2009). Ammonium-nitrogen is also the dominant form of nitrogen in all substrates in this study. The significantly higher
levels of ammonium that are found in the peat substrate may
be due to the higher amount of organic nitrogen matter associated with peat. Low levels of ammonium-nitrogen are
Geo-Eco-Marina 17/2011
G. Cott, D. Reidy, D. Chapman, M. Jansen – Saltmarshes on peat substrate on the southwest coast of Ireland: edaphic parameters and plant species distribution
characteristic of aerobic, coarser textured soils such as sand
(Hazeldon and Boorman, 1999). Indeed, this study found that
the sand has significantly lower ammonium content than the
peat substrate. Nitrification is dependent on the aeration and
pH of the soil. Nitrification has a pH optimum of 7 to 8 and is
an oxygen dependant process (Sprent, 1987). Fringe marshes
that are characterized by low pH as well as low soil oxygen
due to water saturation are therefore expected to be low in
nitrate- nitrogen. The pH of the peat substrate in this study
however may not be low enough to inhibit nitrification because the nitrate content of the peat is in fact higher than in
the other substrates.
The high moisture content of peat observed in Figure
3(a) also influenced the relationship between substrate type
and vegetation. Species such as Juncus maritimus, associated
with the peat substrate in Figure 4 are capable of tolerating
high moisture content and prolonged periods of flooding. In
terms of species distribution Spartina sp. are also capable of
tolerating high moisture levels. However, its location in Figure 4 suggests that pH is a more influencing factor in its distribution than moisture content. It is concluded, therefore, from
this analysis that pH and ammonium are major drivers of vegetation in fringe systems, thus resulting in a distinct community of plant species capable of co-existing in these marshes.
Due to a high water holding capacity, which influences
drainage dynamics, peat substrate can be saturated or semisaturated most of the time (Boelter, 1968). The high moisture content observed in this study reflects this. The mud
substrate also had high moisture content because the mud
in this study was composed of clay and silt particles (Sheehy
Skeffington and Curtis, 2000). Clay also has a high water holding capacity (Mitchell and Soga, 1976). The course texture of
sand permits water circulation and drainage to take place and
therefore the soil moisture content was low for this substrate.
Armstrong et al. (1985) noted that the distribution of A.
portulacoides in the field was along creek banks, which were
exceptional in their high degree of aeration. Sanchez et al.
(1998) showed that, of all the vegetation communities on a
specific marsh, the water table was lowest (–16cm) within the
Atriplex stands. Water-table depth was also negatively correlated with redox potential, but they did not find that tidal
inundation discriminated against A. portulacoides. It would
thus appear that A. portulacoides is incapable of surviving
in continuously waterlogged or excessively wet soils, but
that occasional, short-lived inundation by the tide does not
negatively affect these plants (Sanchez et al., 1998). A. portulacoides and other Atriplex or Atriplex species do not develop
extensive aerenchyma systems (Justin and Armstrong, 1987;
Asad, 2001), showing that they are likely to be intolerant of
waterlogged conditions.
It is clear from the analysis of substrate-linked edaphic
parameters that peat substrate fringe systems differ significantly from saltmarsh systems on other substrates and it is
therefore concluded that fringe systems are distinct systems
based on these parameters.
Canonical correspondence ordination showed that
several edaphic factors were highly influential in determining the relationship between substrate type and saltmarsh
vegetation (Figure 4). Ammonium, nitrate and pH are highly
correlated with axis one. The peat substrate is located on the
positive side of axis one with increasing ammonium levels
and decreasing pH. On the negative side of axis one the sand,
mud and sand/mud substrates are located. This again demonstrates that the peat substrate is markedly different from
the other substrates. Species near the origin include Plantago
maritima, Puccinellia maritima and Aster tripolium. These species occur in all sites, tolerating all four substrates, whilst not
being found on substrates with more extreme pH, nitrate or
ammonium levels or moisture content.
Plant species located at the positive side of axis one,
namely, Juncus maritimus, Juncus gerardii (Juncaceae) and
Triglochin maritima (Juncaginaceae) are most likely to be
found on soils with high ammonium content. Species from
these families are currently widely used in constructed wetlands for the removal of excess nutrients such as ammonium
(Greenway, 2007). Both A. portulacoides and Limonium humile
have the most negative scores and therefore are least likely
to grow in soils high in ammonium and moisture. A. portulacoides is a member of the Chenopodiaceae family, which
are known to be ammonium sensitive (Britto and Kronzucker,
2002). The position of this species in Figure 4 reflects this.
The results of the ex situ growth experiments conducted
in this study largely agree with this. Roots of plants raised in
anaerobic, waterlogged, conditions showed a significant decrease in root length over the five week period during which
they were submerged, and visible damage to the roots could
be seen. Root stress was evident in the form of blackened,
brittle roots. Roots of plants watered only occasionally exhibited the greatest increase in length, again suggesting an affinity for drier conditions.
Biomass is perhaps the most widely used indicator of
plant productivity in salt marsh ecosystems (Jensen, 1985;
Groenendijk and Vink-Lievart, 1987). Biomass accumulation
comprises all above ground and below ground tissue and
does not discriminate against lateral shoots and lateral roots,
unlike the measurement of the longest shoot or longest root.
The overall trend in this study was that growth was highest
on the driest soils. Plants constantly submerged were found
to suffer a loss of biomass; even though there was an increase
in shoot length. The loss of biomass correlated with a loss in
root length. Despite an increase in leaf number many of the
original, larger leaves had been lost and replaced by more,
new, but smaller leaves. Leaf number was found to increase
across all submergence regimes indicating that A. portulacoides is capable of generating new growth despite being
stressed.
Geo-Eco-Marina 17/2011
47
G. Cott, D. Reidy, D. Chapman, M. Jansen – Saltmarshes on peat substrate on the southwest coast of Ireland: edaphic parameters and plant species distribution
This study has shown that in ex situ conditions A. portulacoides shows an affinity for well drained, aerated soils, and
that the duration of submergence has a significant influence
on the growth responses of both its above ground and below ground tissues. However, the results also showed that
the peat substrate had a significantly positive effect on plant
biomass when watered only occasionally. This establishes the
fact that A. portulacoides is capable of primary production
on peat substrate under ex situ conditions in the absence of
competitor species. Generally, plants developed better under
drier conditions, suggesting that this may determine distribution in saltmarshes. Thus, a combination of intolerance
to high soil moisture content, combined perhaps with a decrease in competitive strength may control A. portulacoides
distribution. Indeed, to become established on a fringe marsh
A. portulacoides would have to compete with species that can
tolerate high levels of ammonium and moisture and low pH
i.e. Juncus maritimus. The relatively high moisture content of
peat substrates may therefore comprise a competitive disadvantage. Additionally, our data indicate that other abiotic
and biotic factors such as sensitivity to ammonium may also
play a role in controlling A. portulacoides distribution along
the west coast of Ireland. Previously, Sheehy Skeffington and
Curtis (2000) linked the distribution of A. portulacoides to the
intensive grazing of saltmarshes on the west coast by cattle
and sheep. This study indicates that a combination of multiple abiotic and biotic factors, including intolerance to high
soil moisture levels, is most likely to be responsible for determining A. portulacoides distribution in Ireland
5. Conclusions
The analysis of edaphic parameters shows that peat substrate from fringe systems differs significantly from other
saltmarsh substrates. Canonical correspondence ordination
showed that pH and ammonium were major drivers of vegetation in fringe systems, resulting in a distinct community of
plant species capable of co-existing under fringe marsh conditions. A. portulacoides clearly showed an affinity for drier
conditions under both in situ and ex situ conditions and it is
concluded that its absence from fringe marshes in Ireland is
likely due to a combination of both biotic and abiotic factors,
including intolerance to high soil moisture levels.
References
Adam, P. , 1990. Saltmarsh Ecology. Cambridge University Press, Cambridge.
Allen, S.E., 1989. Chemical analysis of ecological materials, Blackwell,
Oxford.
Allen, J.R.L., 2000. Morphodynamics of Holocene salt marshes: a review sketch from the Atlantic and Southern North Sea coasts of
Europe - Quaternary Science Reviews, V. 19, [12], p. 1155-1231.
Armstrong, W., Wright, E. J., Lythe, S., Gaynard, T.J., 1985. Plant Zonation
and the effects of the spring-neap tidal cycle on soil aeration in
a Humber salt marsh - The Journal of Ecology, V. 73, p. 323-339.
Asad, A., 2001. Adaptation trials of Atriplex and Maireana species and
their response to saline waterlogged conditions in Pakistan - Pakistan Journal of Biological Sciences, V. 4, p. 451-457.
Beeftink, W.G., 1977. The coastal salt marshes of western and northern
Europe: an ecological and phytosociological approach - Ecosystems of the World 1: Wet Coastal Ecosystem, Elsevier Scientific
Publishing Co., New York , p. 109.
Boelter, D.H., 1968. Important physical properties of peat material Proceedings of the Third International Peat Congress, National
Research Council of Canada, Quebec City, p. 150-156.
Britto, D.T., Kronzucker, H.J., 2002. NH4+ toxicity in higher plants: a critical review - Journal of Plant Physiology, V. 159, [6], p. 567-584.
Curtis, T.G.F., Sheehy Skeffington, M.J., 1998. The salt marshes of Ireland:
An inventory and account of their geographical variation - Biology and Environment: Proceedings from the Royal Irish Academy,
V. 98B, p. 87-104.
Dahl, E., Hadăc, E., 1941. Strandgesellschaften der Insel Ostoy im Oslofjord - Nytt Mag Naturvidensk, V. 82, p. 251- 312.
Dormann, C.F., Van der Wal, R., Bakker, J.P., 2000. Competition and herbivory during salt marsh succession: The importance of forb
growth strategy - The Journal of Ecology, V. 88, p. 571-583.
Gorham, E., 1953. A Note on the Acidity and Base Status of Raised and
Blanket Bogs - Journal of Ecology, V. 41, [1], p. 153-156.
Greenway, M., 2007. The role of macrophytes in nutrient removal using constructed wetlands - In: Singh, S.N. and Tripathi, R.D., 2007.
Environmental Bioremediation Technologies, Springer Verlag, p.
331- 352.
Groenendijk, A.M., Vink-Lievaart, M.A., 1987. Primary production and
biomass on a Dutch salt marsh: emphasis on the below-ground
component - Plant Ecology, V. 70, [1], p. 21-27.
Hazelden, J., Boorman, L.A., 1999. The role of soil and vegetation processes in the control of organic and mineral fluxes in some western
European salt marshes - Journal of Coastal Research, V.15, p. 15-31.
Chapman, V.J., 1960. Salt marshes and salt deserts of the world, Leonard Hill Ltd, London.
Huang, S., Pant, H.K., 2009. Nitrogen transformation in wetlands and
marshes - Journal of Food, Agriculture & Environment, V.7, [3&4],
p. 946-954.
Clymo, R.S., Kramer, J.R., Hammerton, D., 1984. Sphagnum-Dominated
Peat Bog: A Naturally Acid Ecosystem [and Discussion] - Philosophical Transactions of the Royal Society of London Series B,
Biological Sciences, V. 305, [1124], p. 487-499.
ISO/TS 14256-1, 2003. Soil quality – Determination of nitrate, nitrite
and ammonium in field moist soils by extraction with potassium
chloride solution, International Organisation for Standardisation,
Geneva, Switzerland.
48
Geo-Eco-Marina 17/2011
G. Cott, D. Reidy, D. Chapman, M. Jansen – Saltmarshes on peat substrate on the southwest coast of Ireland: edaphic parameters and plant species distribution
Jessen, K., 1948. Studies in Late Quaternary deposits and flora history
of Ireland - Proceedings of the Royal Irish Academy, Section B:
Biological, Geological, and Chemical Science, Vol. 52, p. 85-290.
Jensen, A., 1985. On the Ecophysiology of Halimione portulacoides –
Vegetation, V.61, p. 231-240.
Justin, S., Armstrong, W., 1987. The anatomical characteristics of roots
and plant response to soil flooding - New Phytologist, V. 106, p.
465-495.
Kent, M., Coker, P., 1992. Vegetation Description and Analysis: a practical approach, Bellhaven Press, London.
Mitchell, F., 1986. The Shell guide to reading the Irish landscape.
Country House, Dublin.
Mitchell, J.K., Soga, K., 1976. Fundamentals of soil behaviour, Wiley,
New York.
Montemayor, M.B., Price, J.S., Rochefort, L., Boudreau, S., 2008. Temporal
variations and spatial patterns in saline and waterlogged peat
fields: 1. Survival and growth of salt marsh graminoids - Environmental and Experimental Biology, V. 62, p. 333-342.
O‘Connell, M., 1988. Streamstown Bay – partially submerged peat as
evidence for later post glacial sea-level change. In: O’Connell, M.;
Warren, W. (eds) Connemara, Field guide No. 11, Irish Association
for Quaternery Studies, Dublin, p. 44-49.
Sánchez, J., Otero, X., Izco, J., 1998. Relationships between vegetation
and environmental characteristics in a saltmarsh system on the
coast of Northwest Spain - Plant Ecology, V. 136, p. 1-8.
Sheehy Skeffington, M.J., Curtis, T.G.F., 2000. The Atlantic element in
Irish salt marshes - In: Rushton B.S. (Ed.) Biodiversity: the Irish dimension, Proceedings of the Royal Irish Academy Seminar 1998.
Royal Irish Academy Dublin, p. 77-91.
Shennan, I., 1995. Sea-level and coastal evolution: Holocene analogues
for future changes - Coastal Zone Topics: Process, Ecology and
Management, V. 1, p. 1- 9.
Sjörs, H., Gunnarsson, U., 2002. Calcium and pH in North and Central
Swedish Mire Waters - Journal of Ecology, V. 90, [4], p. 650-657.
Sprent, J.I., 1987. The ecology of the nitrogen cycle. Cambridge University Press.
Ter Braak, C.F.J., 1987. Ordination. In: Jogman, R.H.G., ter Braak, C.J.F.,
van Tongeren, O.F.R. Eds., Data Analysis in Community and Landscape Ecology. Pudoc, Wageningen, The Netherlands, p. 91–173.
Van Wijnen, H.J., Van
der
Wal, R., Bakker, J.P., 1999. The impact of her-
bivores on nitrogen mineralization rate: Consequences for salt
marsh succession - Oecologia, V. 118, p. 225-231.
Geo-Eco-Marina 17/2011
49